1. Field of the Invention
This invention relates to a mechanism for operating a needle board in a needling machine, comprising a needle beam for supporting the needle board, two reciprocatory rods connected to the needle beam, two eccentric drives for driving the reciprocatory rods and two bearing housings movably mounting the two eccentric drives, respectively, which bearing housings serve to guide the reciprocatory rods.
2. Description of the Prior Art
To permit the use of larger working widths for the needling of nonwoven webs it is conventional (Austrian Patent Specification 256,491) to provide the needle board means by which the working width is determined as a modular assembly of a plurality of needle boards, and to operate each needle board by two reciprocatory rods connected each to an eccentric drive so that each needle board has associated with it a drive mechanism in which the guides for the two reciprocatory rods and the associated eccentric drives are provided in a common bearing housing, which together with the bearing housings for the remaining needle boards of the needle beam is secured to a carrier, which extends throughout the length of the set of boards. Because the eccentric shafts of each drive mechanism are connected by a flexible coupling, vibration will be restricted to each drive mechanism so that the set of needle boards can be reciprocated at high frequencies even if the working width is large. But said known drive mechanisms have the disadvantage that the common bearing housing for the two reciprocable rods and the associated eccentric drives determine a certain spacing of the lifting rods and thus oppose an adaptation of the lifting rod spacing to a desired length of the needle board. In that connection it must be borne in mind that a deflection of the needle beam which supports the needle board will result in a variation of the depth of penetration of the needles into the nonwoven web across the length of the needle beam so that the nonwoven web will not be regularly needled. For this reason the deflection of the needle beam must be kept within very close limits and this gives rise to the requirement that the rod spacing must be adapted to the length of the needle board, so that a rod spacing will permit the working width to be selected only in certain steps.
If the reciprocatory rods and the associated eccentric drives are not mounted in common bearing housings and each reciprocatory rod and the associated eccentric drive are accommodated in a separate housing, it will no longer be possible to benefit from the advantages afforded by the provision of a common housing particularly as regards the taking up of vibration. On the other hand, drive mechanisms provided with two separate housings for respective rod drives will permit an adaptation of the rod spacing to the length of the needle beam. The resulting vibration problems will have the result that needling machines provided with such drive mechanisms can be reciprocated only at a relatively low frequency.